Spring brake units

ABSTRACT

A spring-actuated fluid pressure-released brake unit for use in a hydraulic braking system comprises a mounting plate embodying and supporting a hydraulic cylinder and piston assembly, an actuating spring and a spring relaxing device, the arrangement being such that all reaction to braking force is taken by the mounting plate so permitting the use of a lightweight shell or casing.

United States Patent 1 Page et al. Nov. 27, 1973 [5 SPRING BRAKE UNITS3,086,745 4 1963 Natho 92 130 x 3,495,503 2/1970 Gummcr et 31.... 92/63[75] lnvenmrs- Wilbur Mlns 3,179,055 4 1965 Kalert 92 128 X CharlesThomas Rlley, North 3,188,048 6/1965 Sutherland..... 92/130 x Hykeman,both ofEngland 2,215,546 9 1940 Dick 188 170 2,401,378 6/1946 Smith92/164 [73] Ass'gnee W)": if g 3,033,325 5 1962 Tjemstrom 188/1703,250,183 5/1966 Gephart 92/130 x 22 Filed: Mar. 1 1971 3,334,545 8/1967Houser 92/130 X 3,462,986 8/1969 Cox et al. 92/63 [21] Appl. N0.:125,597

Primary Examiner-Martin P. Schwadron AssistantExaminer-Allen M Ostra er[30] Foreign Application Priority Data g Mar. 26, 1970 Great Britain14,752 70 Ammey Nms & Batman 52 US. Cl. 92/130 [57] AfBSTRACT 51 Int.Cl. F16d 65/24 A smug-actuated f presute-released brak [58] Field ofSearch 92/63, 130, 64, 170, for In a y li ak ng System comprises a92/171, 128; 188/170 mounting plate embodying and supportlng a hydraulic1 .cylmder and piston assembly, an actuating sprmg and [56] ReferencesCited a spring relaxing device, the arrangement being such UNITED STATESPATENTS that all reaction to braking force 15 taken by the 3 107 58310/1963 w d d 92/63 mounting plate so permitting the use of alightweight 00 war 3,401,606 9/1968 Mathews et a1 92/63 ux or casmg'3,424,062 1/ 1969 Gummer et a1 92/63 7 Claims, 1 Drawing Figure"11111111111111lllillllhlllllllll iilllllllllllllllilllllll PATENTEDHUVNm5 3.774.507

INVENTORS WILBUR MILLS PAGE CHARLES THOMAS RILEY NORRIS & BATEMAN SPRINGBRAKE UNITS This invention relates to vehicle braking apparatusincorporating spring brake units, that is, brake units comprising aspring-loaded piston and cylinder device of which the piston isoperatively connected to the brakes or brake linkage and is acted uponby a supply of pressurised fluid such that the piston is normally heldin an inoperative position, but, upon failure of the fluid pressuresupply, moves under the action of the loading spring to apply thebrakes.

The present invention is concerned more particularly with brakingsystems where hydraulic pressure is used to hold the spring brake unitinoperative, the object of the invention being the provision of animproved form of unit in which the reaction of the applied brakingeffort is exerted directly on the mounting plate or flange of the unit,that is, it is not transmitted through the shell of the unit, withadvantages in economy and rigidity.

According to the invention the improved spring brake unit comprises ashell or casing attached at one end to a mounting plate or flange havinga hollow reentrant portion extending into the shell and defining ahydraulic cylinder, a hollow piston rod guided for axial movement insaid re-entrant portion and carrying a piston movable in the hydrauliccylinder, a coiled compression spring contained within the shell andloading the piston rod in one direction and a thrust rod havingoperative connection at one end with the piston rod and extendingthrough the other end of the shellfor connection to the brakes or brakelinkage. Preferably the inner end of the thrust rod engages an abutmentcapable of controlled displacement along the piston rod thereby to relaxthe compression of the loading spring and provide manoeuvrability of avehicle after automatic brake application following a hydraulic failure.

A preferred embodiment of the invention will now be described withreference to the accompanying drawing which is an axial section throughthe improved spring brake unit, said unit comprising an outercylindrical shell 1 with an integral closure In at one end, the otherend thereof being secured to a plate or flange structure 2 which servesto mount the unit on the framework of a vehicle. The mounting plate 2includes a hollow reentrant portion 3 which extends axially into theshell 1 and is of stepped formation to define two co-axial bores ofdifferent diameters 4, 5. Having sealed axial sljiding movement in thesmaller bore 4 is ahollow piston rod 6, whilst secured onto the end ofsaid rod by a nut 7a is an annular piston 7. sliding in the larger bore5 which constitutes a hydraulic cylinder. A heavy coil compressionspring 8 is interposed between the mounting plate 2 and an abutment ring9 secured to theinner end of the piston rod 6, whilst a thrust rod 10extending through the closed end 1a of the shell is socketed into theinner end of the piston rod 6 to transmit the thrust thereof to thebrake linkage. Brake actuating thrust rod 10 is continually biasedtoward the right in the drawing in the brake release direction by theusual brake return springs (not shown) in the brake linkage. To thisextent the thrust rod is operated conventionally and similarly to thebrake actuating rod disclosed in Gummer et al US. Pat. No. 3,424,062. Inthe arrangement shown a retaining ring 11 received in a peripheralgroove in the thrust rod abuts a stop collar 12 located between ashoulder on the piston rod and a circlip 13 but any equivalentarrangement may be employed which will permit relative pivotal movementof the thrust rod relative to the piston rod. Formed in the mountingplate 2 and re-entrant portion 3 is a passage 14 by which the inner endof the hydraulic cylinder 5 is connected to a hydraulic supply port 15.Thus, in use, hydraulic pressure transmitted to the inner end of thehydraulic cylinder 5 will hold the hydraulic piston 7 in the retractedposition shown against the action of the compressed loading spring 8,whilst a failure in the hydraulic circuit will result in a loss ofpressure in the hydraulic cylinder so permitting the loading spring toexpand and displace the piston rod and effect application of the brakes.

With the construction as so far described it will be apparent that thethrust rod 10 needs normally to be rigidly located relative to thepiston rod 6 in order to transmit the thrust of the spring 8 to thebrake linkage under emergency conditions. However, as previouslymentioned, it is also desirable to be able to release the compression onthe spring 8 to restore manoeuvrability to a vehicle after emergencyapplication of the spring brakes and the present construction embodies asimple mechanism which achieves both objects. As shown, the outer end ofthe piston rod 6 is screw-threaded internally to receive a release bolt16 the inner end of which normally abuts the domed inner end of thrustrod 10. The head of bolt 16 is located externally of the hydrauliccylinder 5, which is closed off by a flexible gaiter 17, said bolt headand the gaiter being enclosed by a sheet metal or plastics cap 18detachably secured to the mounting plate 2 by a circlip or equivalentmeans. An opening in the outer wall of the cap 18 is closed by aremovable rubber or plastics cover 19 and thus when it is required torelax the spring compression after an emergency brake application it ismerely necessary to uncover the head of the release bolt 16 and tounscrew the bolt. Initially, such unscrewing of the bolt will allow thethrust rod 10 under the influence of the usual brake return springs tofollow in abutment with the inner end of bolt 16 and travel along thehollow piston rod 6 and, as the spring is released, the hydraulic piston7 travels along the cylinder 5 toward the end wall thereof. Furtherunscrewing of the bolt 16 allows the thrust rod 10 to continue itsmovement along the piston rod 6 until a sufficient effort is relaxedfrom the brakes or brake linkage to allow vehicle mobility.

When the brakes are applied by loading spring 8 under the emergencycondition represented by failure of pressure in the hydraulic cylinder,the piston 7 moves to the left in the drawing. it normally does nottravel the entire length of cylinder 5 but is moved only sufficiently toapply the brakes. Thus, the brakes having been applied, there is stilladequate room for further travel of the piston relative to the thrustrod to release the thrustlrod from the force of loading spring 8.

Actually in practice the piston 7 would almost never abut the end wallof cylinder 5 because energization of spring 8 would be' released beforethe piston reached that positon.

The spring relaxing device is also of considerable assistance whenfitting the spring brake unit to or removing it from a vehicle in thatall load can be relaxed when required to facilitate assembly ordismantling of yokes, pins and equivalent linkage connections, thespring loading being restored when desired without any danger to theoperator. 1

As the whole of the mechanism is carried on and supported by themounting plate 2 it will be apparent that all braking reaction is takenby said plate and the casing l which merely acts as a protective covermay therefore be of relatively light construction. In the embodimentshown the casing which is formed of a plastics material or of sheetmetal has a push fit into an expanding pressed steel retainer secured tothe mounting plate 2, the casing having a moulded-in beading 21 whichsnaps into a complementary groove in the retainer and the casing beinglocked in this position by a releasable wire type clip 22 or anyequivalent means.

We claim:

1. A spring brake unit for use in a vehicle braking system comprising ahollow member containing a hydraulic cylinder, a piston slidable in saidcylinder, a hollow piston rod fixed to said piston and axially slidablyextending through one end of said member, a compression spring disposedbetween said member and said piston rod, said spring being compressed toenergized condition when said piston rod is moved in the brakes-offdirection by hydraulic fluid pressure in said cylinder, and saidcompressed spring in the absence of predetermined hydraulic pressure insaid cylinder acting to displace said piston rod in the brakes-ondirection, means providing an axial abutment within said piston rod, avehicle brake actuating thrust rod extending through said hollow pistonrod into operative engagement within said abutment, and means accessibleat the other end of said member for effecting controlled displacement ofsaid abutment along the piston rod toward said other end of said memberthereby permitting said thrust rod to follow the abutment and move inthe brakes-off direction.

2. The spring brake unit defined in claim 1, wherein said membercomprises a mounting plate for attachment to vehicle structure and ahollow projection on said plate containing said hydraulic cylinder.

3. The spring brake unit defined in claim 1, wherein said member is amounting plate and a shell enclosing said piston rod and spring isremovably secured to said plate, said plate having a reentrant hollowportion extending within the shell and containing said hydrauliccylinder, said piston rod at one end being slidable in said reentrantposition, and said thrust rod extending slidably through said shell intosaid hollow piston rod.

4. The spring brake unit defined in claim 3, wherein said piston rod hasa flange at its said one end outside the reentrant portion of saidmember, and said spring is a coiled spring extending between said flangeand said mounting plate.

5. In the spring brake unit defined in claim 1, said abutment having ascrew threaded mounting within said piston rod and having an operatinghead outside the piston rod.

6. A spring brake unit as defined in claim 5, wherein said abutment is abolt threadedly mounted within said hollow piston rod, and a removablecover is provided on said member providing access to the bolt head.

7. A spring brake unit as defined in claim 3, said shell being ofrelatively light weight plastics or sheet metal.

1. A spring brake unit for use in a vehicle braking system comprising ahollow member containing a hydraulic cylinder, a piston slidable in saidcylinder, a hollow piston rod fixed to said piston and axially slidablyextending through one end of said member, a compression spring disposedbetween said member and said piston rod, said spring being compressed toenergized condition when said piston rod is moved in the brakes-offdirection by hydraulic fluid pressure in said cylinder, and saidcompressed spring in the absence of predetermined hydraulic pressure insaid cylinder acting to displace said piston rod in the brakes-ondirection, means providing an axial abutment within said piston rod, avehicle brake actuating thrust rod extending through said hollow pistonrod into operative engagement with said abutment, and means accessibleat the other end of said member for effecting controlled displacement ofsaid abutment along the piston rod toward said other end of said memberthereby permitting said thrust rod to follow the abutment and move inthe brakes-off direction.
 2. The spring brake unit defined in claim 1,wherein said member comprises a mounting plate for attachment to vehiclestructure and a hollow projection on said plate containing saidhydraulic cylinder.
 3. The spring brake unit defined in claim 1, whereinsaid member is a mounting plate and a shell enclosing said piston rodand spring is removably secured to said plate, said plate having areentrant hollow portion extending within the shell and containing saidhydraulic cylinder, said piston rod at one end being slidable in saidreentrant position, and said thrust rod extending slidably through saidshell into said hollow piston rod.
 4. The spring brake unit defined inclaim 3, wherein said piston rod has a flange at its said one endoutside the reentrant portion of said member, and said spring is acoiled spring extending between said flange and said mounting plate. 5.In the spring brake unit defined in claim 1, said abutment having ascrew threaded mounting within said piston rod and having an operatinghead outside the piston rod.
 6. A spring brake unit as defined in claim5, wherein said abutment is a bolt threadedly mounted within said hollowpiston rod, and a removable cover is provided on said member providingaccess to the bolt head.
 7. A spring brake unit as defined in claim 3,said shell being of relatively light weight plastics or sheet metal.